1. Field of the Invention
The present invention relates to a fuel cell, and more particularly, to a power supply apparatus and method for a line connection type fuel cell system which can improve operating efficiency and economical efficiency of the fuel cell system by automatically controlling an output current of a fuel cell to be maximized.
2. Description of the Background Art
In general, a fuel cell is an apparatus for directly converting energy of fuel into electric energy. In the fuel cell, an anode and a cathode are installed at both sides of a polymer electrolyte film. Electrochemical oxidation of hydrogen, which is a fuel, is generated in the anode (or oxidation electrode), and electrochemical deoxidation of oxygen, which is an oxidizing agent, is generated in the cathode (or deoxidation electrode). That is, the fuel cell generates electrons by the electrochemical oxidation and deoxidation, and generates electric energy by movement of the electrons.
Exemplary fuel cells include a phosphoric acid fuel cell, an alkaline fuel cell, a proton exchange membrane fuel cell, a molten carbonate fuel cell, a solid oxide fuel cell, and a direct methanol fuel cell. In addition, the fuel cells can be classified into a commercial fuel cell, a home fuel cell, a vehicle fuel cell for an electric vehicle, and a small-sized fuel cell for a portable terminal or a notebook computer by used fields. Especially, the home fuel cell has been improved to efficiently operate an electric home appliance or a lighting apparatus in a house, and the commercial fuel cell has been improved to efficiently operate a lighting apparatus, a motor or a machine in a shopping center or a factory.
The fuel cell system is linked with a line power supply system (e.g., a public power company). If power supplied to a load is deficient, the fuel cell system is supplied with the deficient quantity of power from the line power supply system, and if power supplied to the load is too much, the fuel cell system supplies the surplus power to the line power supply system.
FIG. 1 is a block diagram illustrating a conventional power supply apparatus for a line connection type fuel cell system. Referring to FIG. 1, the conventional power supply apparatus includes a fuel cell 1, a power converting unit 2, and a line power supplying unit 3. The fuel cell 1 includes a stack (not shown) comprised of an anode and a cathode for generating electricity by electrochemical reactions of hydrogen and oxygen, and generates a DC voltage from the stack (not shown). The power converting unit 2 includes a DC/DC converting unit (not shown) for converting the DC voltage into an AC voltage, boosting or dropping the AC voltage, rectifying the resulting voltage, and outputting a DC voltage. The power converting unit 2 also includes an inverter (not shown) for converting the DC voltage from the DC/DC converting unit into an AC voltage.
The line power supplying unit 3 supplies common power to each house or public facility (load). That is, the fuel cell system and the line power supplying unit 3 are linked to each other, for supplying power to each house or public facility.
In the case that power generated in the fuel cell system is sold to a public power company (line power supplying unit), if a current outputted from the fuel cell 1 is larger than a preset maximum output current, the current is decreased. In addition, in the case that power generated in the fuel cell system is sold to a public power company (line power supplying unit), if a voltage outputted from the fuel cell 1 is lower than a minimum output voltage, the output current of the fuel cell 1 is decreased. That is, the conventional fuel cell system maintains at least a specific minimum output voltage of the fuel cell.
However, even if the output voltage is lower than the probable minimum voltage, if the output current is reduced, the fuel cell system is stably operated. Nevertheless, when the output voltage of the fuel cell is lower than the probable minimum voltage, driving of the fuel cell is stopped, which narrows an operating available width of the fuel cell system. As a result, operating efficiency of the fuel cell system is reduced.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced.